Abstract
A series of N-methyl quaternized derivatives of poly(4-vinylpyridine) (PVP) were synthesized in high yields with different degrees of quaternization, obtained by varying the methyl iodide molar ratio and affording products with unexplored optical and solvation properties. The impact of quaternization on the physicochemical properties of the copolymers, and notably the solvation properties, was further studied. The structure of the synthesized polymers and the quaternization degrees were determined by infrared and nuclear magnetic spectroscopies, while their thermal characteristics were studied by differential scanning calorimetry and their thermal stability and degradation by thermogravimetric analysis (TG-DTA). Attention was given to their optical properties, where UV-Vis and diffuse reflectance spectroscopy (DRS) measurements were carried out. The optical band gap of the polymers was calculated and correlated with the degree of quaternization. The study was further orientated towards the solvation properties of the polymers in binary solvent mixtures that strongly depend on the degree of quaternization, enabling a better understanding of the key polymer (solute)-solvent interactions. The assessment of the underlying solvation phenomena was performed in a system of different ratios of DMSO/H2O and the solvatochromic indicator used was Reichardt’s dye. Solvent polarity parameters have a significant effect on the visible spectra of the nitrogen quaternization of PVP studied in this work and a detailed path towards this assessment is presented.
Highlights
Quaternized nitrogen involving polymers are a class of highly functional macromolecules that exhibit the properties of conventional polymers and an enhanced sensitivity towards the external environment due to the existing charges, e.g., solvent polarity, pH [1,2]
Methanol was used as a solvent for the synthesis of the fully quaternized polymer (PVPQ), while ethanol was preferred for the partially
Characterization with Fourier transform infrared (FTIR) and Nuclear magnetic resonance (NMR) essentially contributed to the understanding of the structure and composition of the fully (PVPQ) and partially (PVP_Q1-3) quaternized derivatives
Summary
Quaternized nitrogen involving polymers are a class of highly functional macromolecules that exhibit the properties of conventional polymers and an enhanced sensitivity towards the external environment due to the existing charges, e.g., solvent polarity, pH [1,2]. Unique properties are derived from their distinct nature, such as excellent water solubility, strong binding interactions with oppositely charged surfaces and molecules as well as a notable solvation and swelling behavior Due to these features, they are widely employed as viscosity and surface modifiers as well as selective adsorbers. Charged polypyridines constitute a unique class of compounds in which quaternization enables the introduction of permanent positive charges into the backbone, resulting in electron delocalization phenomena that are attributed to the existence of electron-rich pyridines and electron-poor pyridiniums [30,31,32,33] As a result, these polymers exhibit improved molecular properties, such as non-linear optical activity and increased conductivity [5,12,18,34,35,36]. Amphiphilic copolymers containing a quaternized PVP block have been reported [40,41,42]
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